Monosaccharides and polysaccharides such as fructose, glucose and sucrose are abundant materials that can potentially serve as sources of valuable commercial biobased products or intermediates to prepare such products. By biobased, we mean prepared from a plant or animal source. However, monosaccharides such as fructose and glucose are also food components, so conversion of these materials to industrial usage reduces the availability of these saccharides to serve as food stocks. Thus, there is a need to use non-edible saccharides for the production of industrial products.
Soy molasses is a high volume and non-edible byproduct obtained from the production of soy protein isolate and soy protein concentrates from soybeans. It is used mainly for animal feed. Soy molasses is typically produced as about a 50-60% solids soy molasses solution. Sugars constitute about 62 percent of these solids. Sucrose (a disaccharide composed of fructose and glucose), raffinose (a trisaccharide composed of fructose, glucose and galactose), and stachyose (a tetrasaccharide composed of the same monosaccharides) constitute about 96% of the sugar fraction while the monosaccharides fructose and glucose comprise the rest. Saponins which constitute up to about 15% of the solid fraction also contribute saccharides to this composition. Currently, some producers ferment the soy molasses solution to produce methane that is used as a fuel.
Soy molasses could serve as a source for producing value-added biobased products which would provide more value than using it as a fuel.
EP 2184270 reports the conversion of glucose, fructose, xylose and sucrose to racemic methyl lactate in yields of 40-60% when these sugars are heated to 160° C. in the presence of methanol and relatively high concentrations of zeolite tin-beta. This zeolite has tin (IV) molecularly incorporated in its structure. The article “Tin-catalyzed conversion of trioses to alkyl lactates in alcohol solutions”, Chem. Commun. 2005, 2716-2718 (Y. Hayashi and Y. Sasaki) described the conversion of dihydroxyacetone (DHA) and glyceraldehyde to alkyl lactates with about 90% yield when heated to 90° C. with primary alcohols in the presence of tin(II) and tin(IV) chloride catalysts. The article “Zeolite H-USY for the production of lactic acid and methyl lactate from C3-sugars”, J. Catalysis 2010, 269, 122-130 (R. M. West, et al.) demonstrated that a zeolite with a low Si/Al composition (Zeolyst-Y) was effective in catalyzing the reaction of DHA and glyceraldehyde with methanol to form methyl lactate when heated to 115° C. when using this zeolite catalyst at relatively high concentrations. However, this catalyst lost activity with continued use due to coking, which implies that it would have limited use in a commercial process for converting DHA to alkyl lactates.
The article “Catalytic conversion of cellulose to Levulinic acid by metal chlorides, Molecules 2010, 15, 5258-5272 (L. Peng, et al.) demonstrated that transition metal chlorides, especially chromium(III) chloride, and aluminum chloride exhibit catalytic activity in converting cellulose and glucose to levulinic acid in 55-65% yield when heated to 200° C. in water. A disadvantage of this process is that the levulinic acid is produced as a very dilute aqueous solution so the relatively high cost to evaporate water detracts from the economics of this process.
In “Dehydration of fructose in non-aqueous media”, D. W. Brown, et al, Chem. Tech. Biotechnol, 1982, 32, 920, fructose was heated in lower alcohols such as methanol in the presence of Amberlyst-15. A yield of 43% 5-methoxymethyl-2-furfural (methoxy HMF) and 47% methyl levulinate was obtained in methanol. The selectivity in making methyl levulinate was only about 42% (where yield equals conversion times selectivity). Furthermore, when other products such as methoxy HMF are made, a fractionation scheme must be developed to remove the other products, which increases the cost of the process.
There is a need for economical processes of converting non-edible saccharides into useful industrial products.